Date post: | 29-Jan-2016 |
Category: |
Documents |
Upload: | loraine-haynes |
View: | 212 times |
Download: | 0 times |
experienceLaurent S. Nadolski
Accelerator Physics GroupOn behalf of the Sources and Accelerator Division
SOLEIL experience, Laurent S. Nadolski 2
Outline
SOLEIL key parameters Linear optics achievements Closed orbit Energy measurement Exploring non-linear beam dynamics
Off axis local orbit bumps Turn by turn data (FMA)
Conclusion
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 3
Storage Ring Optical functions
One of the 4 super-periods
0
5
10
15
20
25
30
0 10 20 30 40 50 60 70 80 s (m)
εx= 3.73 nm.rad at 2.75 GeVC = 354 m w / 4-fold symmetry νx= 18.20
νz= 10.31
20 cm10*ηx
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 4
SOLEIL parameters
OMCM June 20-22, 2011
Parameters Design Achieved as of Dec 2010
Energy ( GeV ) 2.75 2.74
RF frequency ( MHz ), harmonic number h
352.197416
Betatron Tunes 18.20 / 10.30 18.202/10.310
Natural Chromaticities -53 / -23 -51/-21
Momentum Compaction α1 / α2 4.5 x 10-4 / 4.6 x 10-3
4.5 x 10-4 / 4.6 x 10-3
Emittance H ( nm.rad ) 3.73 3.73
Energy spread 1.016 x 10-3 1.016 x 10-3
Coupling, εV/εH<1% 0.3% (without correction)
Current Multibunch mode ( mA ) 500 500 (400 for Users operation)
Average Pressure ( mbar ) 1 x 10-9 1 x 10-9 @ 500 mA
Beam Lifetime ( h ) 16 h 20h @ 400 mA / 14h @ 500 mA
Single bunch current ( mA ) 12 20
Beam position stability, mm ( H ) 20 (rms) 3 peak to peak (top-up)
Beam position stability, mm ( V ) 0.8(rms) 1 peak to peak (top-up)
SOLEIL experience, Laurent S. Nadolski 5
Linear optics modelling with LOCO: SOLEIL caseLinear Optics from Closed Orbit response matrix
J. Safranek et al.
Quadrupole gradient variation
Modified version of LOCO with constraints on gradient variations
Due to lattice compactness (see ICFA News letter, Dec’07)
β- beating reduced to 0.3% rms
Results compatible with mag. meas. and internal DCCT calibration of individual
power supply
Hor. dispersion
Hor. β- beating
Ver. β- beating
Quadrupole gradient variation
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 6
Linear Orbit Restoration Beta-beating, tune shift
Compensation Precise but takes machine dedicated time: 30 min Static (e.g. LOCO) or Dynamics (e.g. feedforward systems)
Local or global compensation for perturbations induced by IDs IDs are freely controlled by users, many different combinations:
the storage ring is alive! Need of a global tune feedback. Excitation through FBT on a single bunch
Impedance induced tune-shift with current intensity (coherent and incoherent) How to correct for it (locally, globally?)
Necessary steps for going to low coupling value and fine resonance correction
Is it possible to get online measurements during user operation? Tracking beta beating for all ID configurations (21 IDs in 2011)? How to get LOCO precision with turn by turn data?
Use of residual orbit distortion during top-up injection
How to get enough turns while a TFB is running?
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 7
ξxnat ξz
nat
Model -51 -21
Measurement -49 -19
Measurement of dipole fieldperformed using NMR probe.
Natural chromaticities
1. Varying bending magnet field: feasible2. Switching off sextupole magnets:
unfeasible for large ring
Two main methods
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 8
Natural chromaticities:How much do we trust tracking codes?
Interesting experiment performed at LNLS (Brazil, Campinas)
2 methods are fully not equivalent Do tracking codes systematically overestimate chromaticity?OMCM June 20-22, 2011
-0.6 +2
SOLEIL experience, Laurent S. Nadolski 9
Measuring the electron beam energyby spin depolarization: difficulties
Polarization build up nicely observed using Touschek lifetime as a polarimeter
Polarization time: 17 min as expected
Beam depolarization
E ≈ 2.7385 GeV but at 0.1% (very wide dep. frequency range)
Beam energy measurement by spin depolarization is not an easy task: success in ALS, ANKA, BESSY II, SLS, … not for the last built light sources!
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 10
Orbit feedback systemsCorrection Down to DC
• How to make slow and fast orbit feedback systems work together?
• Slow and fast orbit feedback systems are not compatible if they have a common frequency domain:– Both systems fight each other (120 BPMs, 56 slow, 32 fast in both planes)– The weakest correctors from FOFB saturate after a few iterations of the slow
system– Since April 2009, both feedback systems work in harmony
– FOFB (10 kHz, 360 µs latency time) around residual closed orbit of SOFB– SOFB make to zero the average current of fast dipolar correctors
– Stability reached: 650 nm RMS in H-plane 200 nm RMS in V-plane
Frequency (Hz)1 1010-110-2DC
SOFB FOFB
DEAD
BAND
Dead band approach not suitable• FOFB efficiency is suppressed at low
frequencies (< 0.1 Hz)• ID motion frequency band
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 11
Beam position stabilityOrigin of some noise around 50 Hz identified:
Air fans which cool the ceramic vessels at different places of the ringNoise level extremely now in vertical plane to 200 nm (0-500 Hz)
Vertical noise spectrum from BPMHorizontal noise integrated from BPM
Shaker
Kickers
FCT
650 nm RMS 200 nm RMS
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 12
Off axis integralsProbing non linear dynamics of IDs
Orbit distortion
First order effect induced by ID imperfections
Second order due to oscillating trajectory of the electrons (computed by RADIA code)
Good agreement with magnetic measurement if dynamic effects are deduced
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 13
-30 -25 -20 -15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
20On beam measurements
RADIA 2nd order field integral
Magnetic measurements
RADIA + Magnetic measurements
x (mm)
Ver
tical
Fie
ld I
nteg
ral (
G.m
)
Magnetic correction was done to compensate for the 2nd order field integral
The measured residual field integral seen by the beam at large horizontal amplitudes shows that the compensation has to be improved
In-vacuum 2T wiggler
How is it used?1. Validation of magnetic measurements2. Design of set of magic fingers for compensation of non linear effects
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 14
BPM nonlinear responseBellow
21° water cooling circuitSMA
Feedthroughs
ButtonsMechanical references
Xread < 8 mm
Poisson 2DBoundary Element MethodTRISTAN, DAΦNE, DIAMOND
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 15
Equipment for turn by turn experiments
Since August 2007, the 12 meter long injection section of the SOLEIL storage ring is equipped with one horizontal and one vertical machine study kicker (or pinger magnets)
Active Length Angle B nom Plateau mm mrad mT ns
Kicker H 600 2 30.56 420 Kicker V 300 0.6 18.33 456
The pingers have an excellent reproducibility (10-3 ) and linearity of the magnetic field.
Thanks to their Libera electronics, the 120 BPMs can run at 846 kHz in turn-by-turn acquisition
The standard filtering, optimized for the slower acquisition rates does not fully decouple the position of a specific turn from its previous and following ones. A new filter isolating each turn position will be fully implemented in the coming months.
In the linear region ( ± 4 mm) , the BPM resolution is better than 3 µm RMS
BPM Electronic Module : Libera from Instrumentation Technologies
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 16
The energy acceptance of the bare machine is large : +/- 4%.
Off-momentum FMA experiments have confirmed calculation results
Calculations
dp/p = + 4 % :
3νx=55.
dp/p = + 3 % :
2νx+νz=47
dp/p = - 3 % : 2νx–
νz=26
Measurements
Simulations
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 17
Non linear dynamics• Today FMA like techniques• Are precious tools for diagnosis non linear beam dynamics for both on and
off momentum particles• Guide optimization strategy for increasing accelerator performance• Start being exploited for resonant driving term minimization
• Future: novel design and improvement of diagnostics• Turn by turn data: small crosstalk, better resolution • BPM resolution for large amplitudes• Is it time for individual power supplies for sextupoles?• SOLEIL: strong limitation for probing off-momentum dynamics. Large RF
frequency shifts make aging the cold tuning system of the superconductive cavities• A special cavity for kicking the beam energy over one turn would be very valuable
OMCM June 20-22, 2011
SOLEIL experience, Laurent S. Nadolski 18
Conclusion
Linear optics is well understood
Still a lot of work for tuning complex lattices with many sextupole families, trends to introduce octupole magnets to control tune shift with amplitude, second order chromaticity, increase longitudinal energy acceptance
Non-linear optics correction and measurement based on turn by turn data is still challenging and requires improved BPM systems
individual sextupole PSs?
Other challenging parts Maintaining performance with many insertion devices freely controlled by
users. Fast switching devices, low beam sizes drive orbit feedback improvement Local control of beam sizes
Top-up operation means beam delivered over many day period of timeDevelopment of on-line continuous tools to measure beta-beats, chromaticity evolutions, local coupling, performance degradation
but without perturbing the user experiments
OMCM June 20-22, 2011